Lock up your exercise machines! Or at least continue to use them as towel racks. Because they could kill you. So suggests Andrew Marr, who partly blames newspaper articles (sorry, Andy) about the virtues of intensive exercise for the stroke he suffered after an all-out session on his rowing machine.

“I had a strange feeling afterwards,” he told his own stand-in on his Sunday morning TV show. “A blinding headache, and flashes of light... I woke up the next morning lying on the floor unable to move.”

On the same day, Lionel Shriver, of needing to talk about Kevin fame, told The Sunday Times about her regimen of “130 press-ups... 200 side crunches, 500 sit-ups and 3,000 star jumps”. How many?! The jumps take 32½ minutes, the writer explained, or three every two seconds. Guys, what’s wrong with a leisurely swim?

Marr’s right about newspapers. I wrote only this month about the Tabata Protocol, a four-minute workout of extreme, 20-second bursts devised by a Japanese professor. The first reader comment online said: “You should have a very well-trained heart for that kind of exercise. Otherwise you can die. Unexpectedly.”

Not so, say fitness experts, who accuse Marr of perpetuating Hollywood myths about the fragility of the heart. “It was sad he made associations between two events which can’t be made,” says Jamie Timmons, professor of systems biology at Loughborough University’s School of Sport, Exercise and Health Sciences. “The reasons for a stroke and vessel rupture are related to long-term processes. Given the history he has provided, such as smoking, it’s clear he was high-risk. To say it’s down to one event is misleading.”

Timmins says that apart from saving time, high-intensity training is more efficient at processing stuff such as sugar, reducing the risk of developing diseases including diabetes. He cites a study in which 4,500 people already at risk of heart disease were put on a high-intensity fitness program, and were all fine. “I’d hate to think people were discouraged,” he says, suggesting a much greater risk to the nation’s health if they were.

What about Shriver’s workout? “Wow, it takes a very special personality to do that,” he says. “And probably no neighbours.”

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